LED lighting is gradually replacing the traditional incandescent lamp and CFL because of its advantages of energy efficiency, long life and non-pollution aspect. It is now common to see Triac dimmers used in conjunction with traditional incandescent lamps. The principle of triac dimmers is to control the thyristor conduction by the triac dimmer's inner time delay circuit. The longer the conduction time, the more energy is transmitted achieving higher brightness output for incandescent lamps.
The luminosity principle of incandescent lamps is through the production of thermal radiation which in turn emits visible light via the tungsten filament. Its equivalent to a purely resistance load in electricity. Therefore, triac dimmers suit incandescent lamps perfectly, allowing users to adjust the brightness output as needed. Due to the characteristic of thermal radiation, the color temperature of incandescent lamps will decrease from 2700 Kelvin temperature to about 2000 Kelvin temperature when the brightness output is low, which is close to the color temperature at sunset.
Through evolution in technology, LED lamps can also be compatible with traditional triac dimmers. LED lamps can achieve smooth and linear adjustment of brightness by controlling a triac dimmer. However, due to the LED's luminescent properties, the color temperature of LED lamps will not change with a change in driver current. In order to achieve a change in color temperature similar to an incandescent lamp, LED technology uses two or more color temperature variations of LED chips, generally 3000 Kelvin temperature and 2000 Kelvin temperature chips. The current ratio mix is adjusted for the different LED chips allowing the light fixture to achieve this function. Using this advancement in technology, triac dimmers can adjust the brightness output and color temperature concurrently.
Color temperature can be described in terms of the color emitted by a light fixture with a spectrum from bright light, such as daylight, to warm soothing amber light such as at dusk. LED light sources do not exhibit visible spectrum radiation at all wave lengths of the spectrum and are measured according to a correlated color temperature (CCT) scale. It would be desirable to be able to operate LED light sources to produce variable color from bright white to amber tone while maintaining bright luminosity. Such would create a light environment which is warm, cozy and relaxing such as is desirable during dinning or working late over a desk top or in front of a computer. It is well known that bright light stimulates the senses of a person and can be disruptive to a person's health particularly when exposed to bright light at night time creating the effect of jet lag, poor sleep and lack of energy during the day. It could also lead to other adverse conditions such as disruption of vital hormone production.
There is therefore a need to provide a dimmable LED light fixture, in the form of lamps or luminaires, and method of operation capable of overcoming the above mentioned disadvantages of LED lighting and thus providing an LED light environment wherein the Kelvin temperature of the LED light source is down to about 3000 to 2000 Kelvin while maintaining maximum brightness.